1. Field of the Invention
The present invention generally relates to a polymer-type polymerization initiator and particularly to such a polymer-type polymerization initiator suitable as a component or material for producing a surface active polymer which is useful as coating agent, surface modifying agent, polymeric compatibilizer, etc.
2. Related Art Statement
In recent years, various sorts of polymers having various properties and functions have been needed. In this background, it has been considered to use a block copolymer or a graft copolymer for modifying a polymer, or enhancing compatibility of one sort of polymer and another sort of polymer, by utilizing the specific properties of the copolymer.
Known graft copolymer-producing processes are such as: i) polymerizing one sort of monomer in the presence of a polymer made from another sort of monomer by utilizing the chain transfer reaction, and thereby producing a graft copolymer (chain transfer method), ii) oxidizing a main-chain polymer with oxygen or ozone to produce active sites in the main-chain polymer, and utilizing the active sites for producing a graft copolymer (oxidation graft copolymerization method), iii) producing a graft copolymer by utilizing radiation (radiation graft copolymerization method), and iv) introducing unsaturated double bonds into a molecule of a polymer made from one sort of monomer, and copolymerizing the double bond-containing polymer with another sort of monomer (macromonomer method). However, the chain transfer method i) suffers from low degree of grafting and therefore does not provide a high-performance graft copolymer. The oxidation graft copolymerization method ii) suffers from high tendency of scission of the main-chain polymer due to the oxidation and, in addition, low degree of grafting up to about 10% only. The radiation graft copolymerization method iii) suffers from complicated operations since the method is carried out in vacuum or under an inert atmosphere. The macromonomer method iv) suffers from troublesomeness of production of the macromonomer and, additionally, high dependence of the degree of copolymerization on the molecular weight of the macromonomer.
For overcoming the above indicated problems, a method has been proposed, which provides a graft copolymer by utilizing a polymer-type polymerization initiator containing as a copolymerized component thereof an azo compound or peroxide compound with an unsaturated double bond capable of copolymerization. In such a method disclosed in "Polymer Preprints Japan", Vol. 33, p. 75, p.1059 and 1062, 1984, an azo compound having a methacryloyl group is used as a comonomer for producing a polymer-type polymerization initiator, and the initiator is used for producing a graft copolymer. However, in the case where a large amount of azo compound with an unsaturated double bond capable of copolymerization is used, crosslinking reaction tends to occur among the molecules. Accordingly, only a small amount of azo compound can be used, and therefore this method suffers from low degree of grafting. In addition, generally, an azo compound is an initiator of low efficiency, and this leads to reducing the degree of grafting.
Another method has been proposed, which produces a graft copolymer by utilizing a polymer-type polymerization initiator containing a peroxide group. In such a method disclosed in British Patent No. 1041088, styrene is grafted to copolymer (i.e., initiator) made from methyl methacrylate and t-butylperoxy methacrylate. In addition, Japanese Patent Application laid open for opposition purpose under Publication No. 46-34100 (1971) discloses a method for grafting methyl acrylate to copolymer (initiator) of styrene and di(t-butylperoxy) fumarate. Such polymer-type polymerization initiators are useful in producing a graft copolymer for improving compatibility of polystyrene and polymethyl acrylate. However, in the case where the polymerization initiators are used for producing a surface active polymer having both hydrophobic and hydrophilic sites and capable of, for example, modifying a hydrophobic surface into a hydrophilic surface, there arises a problem that those initiators are insoluble in a hydrophilic monomer, or a polymerization solvent including a hydrophilic monomer, because the initiators are highly hydrophobic. Therefore, this method suffers from difficulty of grafting of a hydrophilic monomer.